Seal for fused-silicate containers.



E. G. KEYES & C. A. KRAUS.

SEAL POB FUSED SILIGATE CONTAINERS.

APPLICATION FILED APB. l0, 1911.

Patented Jan. 16, 1912.

:UNITED STATES PArruvr OFFICE.

raEnEnICx G. KEYES, or BosToN, AND CHARLES A; KEAUS; o'E NEWTON HIGHLANDS,

. MASSACHUSETTS.'

SEAL FOB IE'U'SED-SIZIIJCGAELIE CNTAINEBS.

l Specication of Letters Patent. v Application 'led April 10, 1911. Serial No. 615,966.

Patented Jan. 16,1912.

To all 'whom it may concern Be it known that we, FREDERICK G.

- KEYES and CHARLES A. KnAUs, both citizens of' the United States, and residents, respec- I l fused-silica would have led to its` adoption fused silica which render it so desirable as a fused silica containers with adequate and A permanent vacuum'tight Seals for the leading-in wires.

The transparency of fused silica to the shorter light waves and to ultra -violet waves, constitutes' this material an admirable `one for, many purposes. The mercury: arc is a copious source of ultra-violet rays, and therefore it has become very .desirable tto utilize fused silica in the construction of the containers for mercury arc lamps.k

Moreover, the' strength and toughness of in the construction of other vacuum electric apparatus were it not for the difficulties presented in the construction and malntenance of an adequate vacuum tight seal for the leading-in wires of "such apparatus. The l'ow thermal coeiicient of expansion of silica which'on many accounts is an advantage, and recommends 1t as a materlal for the containers of vacuum electric apparatus,

is one .of the chief factors operating to prevent the use of this material to the extent.

desired, since it has not heretofore been possible to make a fused and hermetical vacuum tight seal, either directlyor indirectly, between the silica and the metalof which the'leading-in connection is composed. Moreover, the high. fusing temperature of silica would render it `practicallyimpossible to seal a metal lead directly to the silica, since even platinum fuses at alower temperature than that at which silica ,be-

comes fully plastic. So far. as we are informed, these inherent physical propertles of material for the construction of containers for vacuum electric apparatus, have heretofore` constituted on the other hand what have' appeared tobe insuperable obstacles to the thoroughly successful utilization ofl silica for these purposes.

The thermal coeilicient of expansion of silica isv only about one-fifteenth of that of platinum, so that it is obvious that direct sealing of a platinum lead to a silica container is impossible even if the diicultydue to the high fusing Iltemperature of silica could be overcome. Nor is there any other metal that can be employed for this purpose or which is capable of being Sealed directly in a silica container. It is true there are` some nickel steel alloys which have a very low coeiiicient of expansion but this is a variable coeliicient which rises with tem-' perature; and again, the melting point of such metals lies well below the melting point of silica. Vacuum-electric apparatus having quartz containers have been con-v structed, the leads being sealed by making a closel mechanical. fit between metal and silica and then sealing this juncture with mercury, and further, reinforcing the joint with wax; but to persons familiar with the construction and operation of vacuum electric apparatus, it is obvious that while temporarily operative, Such sealing-in devices are quite inadequate, especially so as contrasted with the simple and effective sealing which can be securedv between ordinary glass and small platinum leading-in wires. Indeed, the latter has been, so far as We know, the only thoroughly adequate and' ksatisfactory vacuum seal between metal and fra 'le vitreous material.

etare aware that it has been proposed to vary the composition of a silica vacuum electric container by producing a continuous gradation of thefcomposition of -the vitreous material` from thesubstantially pure' silica of which the body of the container is composed down to a lass having a coeilicient of `expansion suihgciently high to make it amenable-.to the sealingV in of a metal lead. It has been suggested thus to admix with the silica of whichthe container is composed'a proportion of calcium and potassium oxids in constantly increaslngv quantity and such a suggestion is embod- Aied in United Statesy Patents Nos. 910,969

and 910,736. `-We do` not know of any instance in which the suggestions of these atents have been carried into practical e ect and we should enpec't that considerable, if

.not insuperable, diiculties would be entweeny glasses fused slllca having a coefiiclent of expansion countered in any attem t to practice the suggestion contained in t ese patent specifications. For instance, it is Well known that both potassiumand calcium when, present even in very small quantities in a glass, produce therein a high thermal coeiiicient of expansion, and we should expect that the presence of very small quantltles of such ingredients in4 a region adjoining substantially pure silica would produce such d1screpancies in rate of-expansion as inevitably to rupture the vessel.

The'lowest thermal lcoefficient of expans1on of any glass heretofore known to us lies in the nei hborhood of 3 10. Be-

aving this ycoeiicient and of .6X 10"-6 no glassesv have been procurable ,or have existed so far as we know. The composition of glasses having a coefficient of expansion hi her than 3.X10- is, of course, well within the knowledgeand skill of those who are familiar with glass manufacture.

It is obvious that any attempt to'fuse a glass having al coelicient of expansion even as low as 3'. 10' directly toJ silica would,

i if the fusion were effected, result lin the development of rupturing stresses as soon as the joint members cooled. In order to construct afused, hermetical vitreous joint, 1t has been necessary for us to produce aglass of which the coeiiicient of expansion, while slightly larger than thatof silica, is not so much greater as to produce rupturing stress on coolin theI joint members. yMoreover,

j the wide lnterval between the fusing point of silica and that of ordinary glass which softens below 500 C., makes it obvious that glasses heretofore-known cannot besuccessfully fused to silica wholly irrespective of the inevitable destruct-ion of such a 'joint (could it be made) by reason of irreconc ilable differences' in coeiicient of expanslon.

We have discovered that if titanium oxid (Ti02) be added to and fused with silicar f in proper proportions, a glass will be produced having suiiciently high melting point and sufficiently low coelicient of expansion as to be adapted to bejoined hermetically.

by fusion to .avessel constructed of pure silica, and-further, that by Aincreasing the proportionl of titanium oxid, the coefficient of expansion of the resulting glass will be raised and its fusing point lowered. The coeiii'cient of expansion of the compound glass can by this means be increased so that lthe resulting composition has a coeicient of expansion in t e neighborhood of that of porcelain. We have discovered also that the propertles of the vitreous composition characterized by a content of titanium oxid may be im roved by the addition of boric voxid (B203 or-vanadium oxid- (V205), and

that both of these ingredients can be added to advantage. The boric oxid facilitates the interfusion of the diiferent ingredients and the vanadium oxid increases the range of viscosity of the resulting glass and toughens the final product. Apparently the presence of titanium oxid and vanadium oxid serves rto fprevent the boric oxid from volatilizing be o re the silica, which forms the basis of the glass, has thoroughly fused and gone into solution.

To compound a titanium silica lass suited to formation of a hermetically sed 'oint with pure silica, we recommend the fo lowing formula: SiO.; 81%', TiO2 7%, V205 3%,

glasses made by the two different formulae,

a glass may be compounded which will make a fused joint successfully with either of the glassesl made according to the formulae above given. Thus, porcelain may be joined and sealed to a vessel made of silica by first fusing the titanium silicate glass of the first formula to the silica itself and then in succession fusing the other two titanium silicate glasses, and finallyl fusing the p0rcelain to the glass representing the second formula above given.v

loo

In order to manufacture joints and seals j Aof lthis character, our preferred mode isv to prepare a number of tubes of the titanium silicate glasses made according to formulae which supply suitably graded steps of expansion-coeicientand tov cut these tubes into rings of suitable'length. These rings may then be fused in succession, the first one to the ltubular end of a vessel composed of silica', and the others in succession, building up a tube composed of successive zones each having a coeiiicient of expansion kslightly higher than that of its predecessor and no vtwo juxtaposed `zones differingy `so largely as to coeicients of expansion as to produce rupturlng stresses.

Our mventlon may be better understood by reference to the drawing hereto annexed which represents'a portion of a mercury-arc lamp` tube with a sealing extension built up of zones' of vitreous material in the manner 'above indicated.

In this-drawing af'represents one end of a fused quartz or silica tube. The face of this tube around its o ening is suitably 'ground off so as to be falrly fiat, and a ring segment b of a titanium silicate glass composed according to the -frst of the above takin ring segments lirst of a "titanium silica e lass made as labove described by using a ormula intermediate between those given in detail, while the segment d iscomposed of a glass made according to the second formula.

In order to provide a suitable Anumber of safe steps or intervals in the ascending' se ries of coeilicientsof expansion, and to provide at the end of the series a glass having a coelicient of expansion high` enough to make an adequate vacuum seal with a leading-in wire, such as n, which may as usual be com.- posed of latinum, the succession of zones or steps om the zone marked d upward may be compounded ats/follows: The zone or ring e is a glass containing 50% of the composition represented by zone d and any sodium-magnesium-borosilicate glass 4of low coelicient of expansion which ma be obtained in themarket. The zone is comof such a borosilicate glass. In compoun ng the glass for zones from g to Z the borosilicate glass is mixed with increasing proportions of common soda or lead glass, these proportions being so .determined that several ldifferences 1n coeili-l cient of expansion between one zone and the next shall lie within safe'limits.' Finally, a cap m of common lead or soda glass is fused to the zone Z and the latinum lead 4n is fused into the cap m. mercury electrode M is introduced intothe tube and the other electrode being similarly provided with a seal of the character justabove described, the apparatus is preparedand com leted in the usual manner. Composite sea s of the above described character will render it feasible tosubstitute silica for glass in any vacuum electric apparatus which has heretofore been constructed of glass.

What we claim and desire to secure by 1. The Combination with a fused silica vessel, of a series of zones of vitreous matej and adapted to, permanent fused juncture with the silica and fused `thereto, the last constituted and adapted ,to seal over a me- `tallic lead, the thermal coefliclents of exansion of the several zones in series graded 1n steps from the first upward, the diversity between the thermal coellicients of any two joined members being less' than that sullicient to produce rupturmg stresses at ,the

junctures.

2,. The combination with a fused silica vessel, ofl a series of zones of vitreous material `fused. in juncture, the first fusedv in juncture with the silica, .being la silica c qualified by a content of titanium oxid, the last constituted and adapted to seal over a metallic lead, and a metallic lead sealed therein, the thermal coelicients of expansion of the several zones vin series being graded in steps from the first upward, the diversity between the thermal coeicients of any two joined members being less than that suli.

cient to produce rupturing stresses at the junctures.

3. The combination with a fused silica vessel, of a series of zones of vitreous material fused in juncture, the first fused in juncture with the silica .being a silica ualified by a content of titanium oxid, an succeeding zones being silica qualiied by vpro-v gressively larger proportions of titamum oxid, the last zone constituted and adapted to seal over a 'metallic lead, the thermal coecients of expansion of the several zones ink series being graded in steps from the flrst'upward7 the diversity between thermal coefficients of any two joined members being less than that suilicient to produce rupturing stresses at the junctures. i

Signed by us at Boston, Massachusetts this third 'day4 of April, 1911.

FREDERICK G. KEYES. CHARLES A. KRAUS Witnesses: ODIN ROBE-nrs, i

CHARLES D. Woonnnnr. 

